Exactly what it sounds
like. The red-purple sputum that is a mixture of cranberry pulp and the excess mucus caused by irritation from drinking the acidic juice. Similar substances can come out of drinking
lemon or
grapefruit juice, but those tend to be a less alarming and therefore noteworthy color.
"Holy
shit, did you just cough up blood?!"
"No, that's just cranberry flem; I
drank some cranberry juice earlier"
"Oh...
Gross"